Polishing cloth and method of manufacturing semiconductor device using the same

ABSTRACT

A polishing cloth used for a chemical mechanical polishing comprises a base body holding a slurry on the surface and serving to mechanically polish the surface of a target object to be polished. Fine particles soluble in a solvent are dispersed in the base body.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a polishing cloth used in achemical mechanical polishing (CMP).

[0002] Recently, a chemical mechanical polishing (CMP) method forflattening a surface of an insulating layer or a wiring layer attractsattentions in this technical field.

[0003] A known polishing cloth used in the CMP method includes“Politex”, (trade name of a polishing cloth manufactured by Rodel Inc.)that does not require a pad conditioning treatment (dressing). Politexhas a cross sectional shape resembling an arrangement of octopus trapsand, thus, is excellent in its capability of retaining a slurry used forthe polishing, said slurry containing water, SiO₂, Al₂O₃, chemicals(oxidizing agent), etc. Also, Politex has a very flexible surface and,thus, does not impart sharp scratches to the surface of the polishedmaterial.

[0004] However, Politex has a very low compression modulus ofelasticity, which is less than 10 MPa, and, thus, is very soft.Therefore, when Politex is used in a flattening process of a targetobject to be flattened, the polishing rate is very low and the flatnessof the target object after the polishing treatment is not satisfactory.

[0005] The known polishing cloth also includes “IC-1000” (trade name ofa polishing cloth manufactured by Rodel Inc.). Voids are formed withinIC-1000. Also, IC-1000 has a compression modulus of elasticity of about200 MPa and, thus, is considerably harder than Politex.

[0006] In general, a pad conditioning treatment using a diamondconditioning plate is applied to the polishing cloth IC-1000 forpolishing a semiconductor wafer. In the pad conditioning treatment, thesurface layer of the polishing cloth IC-1000 is scratched to form a softsurface layer. If the pad conditioning treatment is not applied toIC-1000, IC-100 has a hard surface layer, leading to a low capability ofretaining a slurry and, thus, to a markedly low polishing rate.Naturally, the life of the polishing cloth IC-1000 is determined by thenumber of pad conditioning treatments applied thereto because thesurface layer of the polishing cloth IC-1000 is scratched every time thepad conditioning treatment is applied to the polishing cloth IC-1000.

[0007] Where the polishing cloth IC-1000 subjected to a pad conditioningtreatment is used for polishing 1000 wafers, the surface layer ofIC-1000 is lost in a thickness of about 850 μm. Where the padconditioning treatment is applied under milder conditions to thepolishing cloth IC-1000 for ensuring a longer life of IC-1000, thepolishing rate is lowered or rendered unstable.

[0008] It should be noted that a soft layer having a compression modulusof elasticity of 10 MPa or less is formed in a thickness of scores ofmicrons in the surface region of the polishing cloth IC-1000 immediatelyafter the pad conditioning treatment. The particular soft layer impairsthe flatness on the polished surface of the target object.

[0009] Further, the soft layer is compressed during the polishingtreatment so as to be hardened with progress of the polishing treatment.Since the surface region is hardened, the scratches generated on thesurface region of the polishing cloth IC-1000 are enlarged with progressof the polishing treatment, though the scratch occurrence on the softsurface region is suppressed immediately after initiation of thepolishing treatment.

[0010] As described above, a soft surface layer is formed in thepolishing cloth represented by Politex, with the result that thepolishing rate is low and the polished target object is not satisfactoryin the surface flatness, though scratches are not formed on the targetobject.

[0011] On the other hand, the polishing cloth represented by IC-1000 isdefective in that, if a pad conditioning treatment is not applied to thepolishing cloth, many scratches are formed on the target object withprogress of the polishing treatment. If a pad conditioning treatment isapplied to the polishing cloth, however, the surface region of thepolishing cloth is scratched off. Naturally, the polishing cloth isthinned, leading to a short life of the polishing cloth.

[0012] Further, if a semiconductor wafer is polished by using theconventional polishing cloth for forming, for example, a buried wiring(damascene wiring), dishing or thinning is brought about by anover-polishing so as to generate a so-called “dishing”. The dishingcauses a short-circuiting of the wiring formed in an upper layer in thelithography process. Also, the wiring formed on the dished or thinnedsurface is rendered longer, leading to an increased resistance of thewiring.

BRIEF SUMMARY OF THE INVENTION

[0013] An object of the present invention is to provide a polishingcloth that permits flattening the surface of a target object at a highaccuracy, permits achieving a stable polishing rate, and permitssuppressing the scratch occurrence in the target object, and a method ofmanufacturing a semiconductor device using the particular polishingcloth.

[0014] According to an aspect of the present invention, which isintended to achieve the above-noted object, there is provided apolishing cloth comprising a base body holding a slurry on the surfaceand serving to mechanically polish a surface of a target object to bepolished, and fine particles dispersed in the base body and soluble in asolvent.

[0015] According to another aspect of the present invention, there isprovided a polishing cloth, comprising fine particles soluble in asolvent, and a base body having the fine particles dispersed therein andholding a slurry on the surface, the fine particles being dissolved inthe solvent when a surface of a target object is mechanically polishedby the polishing cloth so as to form concavities on the surface of thepolishing cloth.

[0016] According to another aspect of the present invention, there isprovided a method of manufacturing a semiconductor device by using apolishing cloth, comprising the steps of forming an insulating film on asubstrate, followed by forming a wiring groove on the substrate throughthe insulating film, forming a metal wiring layer on the substrate andin the wiring groove, burying the metal wiring in the wiring groove, andmechanically polishing the metal wiring buried in the wiring groove witha polishing cloth so as to remove an undesired portion of the metalwiring and, thus, to flatten the surface of the metal wiring, thepolishing cloth comprising a base body holding a slurry on the surfaceand serving to mechanically polish a surface of a target object to bepolished, and fine particles dispersed in the base body and soluble in asolvent.

[0017] Further, according to a still another aspect of the presentinvention, there is provided a method of manufacturing a semiconductordevice by using a polishing cloth, comprising the steps of forming agroove in a substrate, forming an insulating film on the substrate suchthat the insulating film is buried in the groove, and polishing theinsulating film by using a polishing cloth so as to remove an undesiredportion of the insulating film, thus, to flatten the surface of theinsulating film, the polishing cloth comprising a base body holding aslurry on the surface and serving to mechanically polish a surface of atarget object to be polished, and fine particles dispersed in the basebody and soluble in a solvent.

[0018] In the polishing cloth of the present invention, fine particlessoluble in a solvent are dispersed in a base body serving tomechanically polish a target object. During the polishing operation, thefine particles exposed to the surface of the base body are dissolved ina solvent such as water to form concavities holding a slurry on thesurface of the base body. It follows that the polishing cloth of thepresent invention permits flattening the surface of the target objecthighly accurately at a high polishing rate. In addition, the scratchformation can be suppressed on the surface of the polished targetobject.

[0019] In the method of the present invention for manufacturing asemiconductor device by using the particular polishing cloth, a wiringgroove is formed in a substrate, followed by burying a metal wiring inthe wiring groove. Then, the undesired portion of the metal wiring isremoved by polishing with the polishing cloth having fine particlessoluble in a solvent dispersed in a base body, thereby improving thequality of the wiring, particularly, a damascene wiring.

[0020] Further, the method of the present invention for manufacturing asemiconductor device by using the particular polishing cloth can also beapplied to the case where an oxide film is buried in place of the metalwiring in the wiring groove. In this case, the oxide film is polished bythe polishing cloth to flatten the surface of the oxide filmsatisfactorily.

[0021] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0022] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0023]FIG. 1 schematically shows the construction of an ideal polishingcloth;

[0024]FIG. 2 is a partial cross sectional view showing the constructionof a polishing cloth according to a first embodiment of the presentinvention;

[0025]FIG. 3 is a cross sectional view partially showing theconstruction of a polished object used for evaluation of a polishingcloth;

[0026]FIG. 4 is a partial cross sectional view showing the constructionof a polishing cloth according to a second embodiment of the presentinvention;

[0027]FIG. 5 is a cross sectional view of a polishing cloth forexplaining the problem taking place by mutual contact of fine particleswithin the polishing cloth;

[0028]FIG. 6 is a cross sectional view showing a gist portion in theprocess of manufacturing a semiconductor device, covering the case wherethe metal wiring in the buried wiring structure (damascene wiring),which is polished by the polishing cloth of the present invention, ismade of aluminum;

[0029]FIG. 7 is a graph showing a dishing occurrence in the case ofpolishing the metal aluminum wiring shown in FIG. 6 with a polishingcloth of the present invention in comparison with the prior art;

[0030]FIG. 8 is a cross sectional view showing a gist portion in theprocess of manufacturing a semiconductor device, covering the case wherethe metal wiring in the buried wiring structure (damascene wiring),which is polished by the polishing cloth of the present invention, ismade of copper;

[0031]FIG. 9 is a graph showing a dishing occurrence in the case ofpolishing the metal copper wiring shown in FIG. 8 with a polishing clothof the present invention in comparison with the prior art;

[0032]FIG. 10 is a cross sectional view showing a gist portion in theprocess of manufacturing a semiconductor device, covering the case wherethe metal wiring in the buried wiring structure (damascene wiring),which is polished by the polishing cloth of the present invention, ismade of tungsten;

[0033]FIG. 11 is a graph showing a dishing occurrence in the case ofpolishing the metal tungsten wiring shown in FIG. 10 with a polishingcloth of the present invention in comparison with the prior art;

[0034]FIG. 12, which is directed to an application of the method of thepresent invention for manufacturing a semiconductor device, is a crosssectional view showing a gist portion in the process of manufacturing asemiconductor device, covering the case where an oxide film buried in agroove formed in a substrate is polished by using a polishing cloth ofthe present invention; and

[0035]FIG. 13 is a graph showing that the oxide removal at the sameremaining step/Å is improved in the case of polishing the oxide filmshown in FIG. 11 with a polishing cloth of the present invention,compared with the prior art.

DETAILED DESCRIPTION OF THE INVENTION

[0036] An embodiment of the present invention will now be described withreference to the accompanying drawings.

[0037] Before describing the embodiment of the present invention, theconstruction of a polishing cloth that is ideal in performance will bedescribed with reference to FIG. 1.

[0038] A polishing cloth shown in FIG. 1 is considered to meet variousrequirements such as a stable polishing rate, a high flatness in apolished surface of a target object, a capability of suppressing scratchoccurrence, and a long life.

[0039] As shown in the drawing, the polishing cloth comprises an innerlayer 51 and a surface layer 52. For ensuring a good flatness in thepolished surface of a target object, the inner layer 51 should desirablybe hard. Also, the surface layer 52 should desirably be soft forsuppressing the scratch occurrence and should desirably be very thin forpreventing the flatness of the polished surface from being impaired.Further, the surface layer 52 should desirably have an appropriatelylarge surface area for allowing the surface layer 52 to hold a slurry.

[0040] A polishing cloth of the present invention meets all therequirements noted above. Specifically, since fine particles aredispersed in a base body in the polishing cloth of the presentinvention, the inner region of the polishing cloth is hard. It should benoted in this connection that voids are formed in the conventionalpolishing cloth IC-1000 as described previously, leading to a hardnesslower than that of the polishing cloth of the present invention.

[0041] In the polishing cloth of the present invention, fine particlesexposed to the surface are dissolved in a solvent, e.g., water, with theresult that fine concavities are formed on the surface of the polishingcloth, leading to a large surface area. Of course, a slurry can be heldsatisfactorily on the surface of the polishing cloth. What should alsobe noted is that the irregular surface resulting from formation of fineconcavities makes the surface region softer than the inner region. Sincethe polishing cloth of the present invention has a soft surface, thescratch occurrence can be suppressed.

[0042] In another embodiment of the present invention, fine particlescoated with a material insoluble in water or slurry are dispersed in thebase body. In this case, even if a plurality of fine particles dispersedin the base body are in mutual contact, all the fine particles incontact with each other are not dissolved in the solvent such as water.If all the fine particles in contact with each other are dissolved in asolvent, large concavities are formed in the polishing cloth so as tosoften even the inner layer of the polishing cloth. In the presentinvention, however, the surface coating permits only the fine particlesexposed to the surface to be dissolved in the solvent. Since all thefine particles in contact with each other are not dissolved in thesolvent, large concavities are not formed in the polishing cloth of thepresent invention.

[0043] Where the solvent is water or slurry, the fine particles newlyexposed to the surface during the polishing operation are dissolved inthe solvent, with the result that deterioration of the polishingperformance is suppressed during the polishing operation.

[0044] A high polishing rate can be obtained where the fine particleshave a diameter of 5 to 30 μm. Some embodiments of the present inventionwill now be described in detail with reference to FIG. 2, et seq.

[0045] [First Embodiment]

[0046]FIG. 2 is a cross sectional view showing the construction of apolishing cloth 10 for CMP according to a first embodiment of thepresent invention. As shown in the drawing, the polishing cloth 10comprises a base body 11 made of, for example, polystyrene and about 25%by weight of fine particles, e.g., water-soluble fillers 12 made ofcellulose, dispersed in the base body 11.

[0047] The base body 11 is hard, and the water-soluble filler 12 is asolid and, thus, is unlikely to be compressed. Therefore, the polishingcloth 10 has a compression modulus of elasticity of 10 GPa or more.

[0048] Those water-soluble fillers 12 which are exposed to the surfaceof the polishing cloth 10 are dissolved in water to form fineconcavities so as to increase the surface area of the polishing cloth10. With increase in the surface area, the surface region of thepolishing cloth 10 is softened so as to prevent scratches from beingformed on the polished surface of the target object. In addition, theslurry can be retained efficiently by the polishing cloth 10.

[0049] The density and depth of the concavities formed on the surface ofthe polishing cloth 10 can be controlled easily by controlling thediameter and the mixing ratio of the water-soluble fillers 12. In otherwords, the conditions of the surface region such as the thickness andsoftness can be controlled easily by controlling the diameter and themixing ratio of the water-soluble fillers 12.

[0050] Table 1 shows the polishing rate and the scratch occurrence,covering the case where an aluminum material containing 0.5% of copperwas polished by the polishing cloth 10 of the present invention as wellas by the conventional polishing cloths of Politex and IC-1000: TABLE 1Polishing Polishing Scratch cloth Conditioning rate occurrence Politexnone 230 nm/min none IC-1000 none  60 nm/min large scratch IC-1000scratch 210 nm/min small scratch Polishing none 205 nm/min none cloth ofpresent invention Polishing scratch 310 nm/min none cloth of presentinvention

[0051] In the case of the conventional polishing cloth of IC-1000, thepolishing rate was 60 nm/min where the conditioning treatment was notapplied thereto, which was markedly lower than the polishing rate of 210nm/min where the conditioning treatment was applied thereto. It isconsidered reasonable to understand that, if a conditioning treatment isnot applied, the surface layer of the polishing cloth IC-1000 wasincapable of sufficiently retaining the slurry, leading to the markedlylow polishing rate.

[0052] On the other hand, the polishing cloth of the present inventionachieved a high polishing rate of 205 nm/min even if the conditioningtreatment was not applied thereto. Clearly, the water-soluble fillersexposed to the surface of the polishing cloth were dissolved in water(slurry) to form fine concavities on the surface of the polishing cloth.As a result, the surface area of the polishing cloth was increased andthe slurry was retained sufficiently on the surface of the polishingcloth, leading to the high polishing rate.

[0053] It should also be noted that the polishing cloth of the presentinvention was found to be stable in the polishing rate. It should benoted in this connection that the water-soluble fillers 12 are newlyexposed to the surface with progress in the abrasion of the surfacelayer of the base body 11 during the polishing operation. Naturally, thenewly exposed fillers 12 are dissolved in the slurry to form newconcavities on the surface of the polishing cloth 10, with the resultthat the polishing rate is kept stable, as pointed out above.

[0054] Further, where a conditioning treatment was applied to thepolishing cloth 10 of the present invention, the polishing rate wasfound to be very high, i.e., 310 nm/min, which is markedly higher thanthe polishing rate in the case where the conditioning treatment was notapplied to the polishing cloth 10 of the present invention or thepolishing rate achieved by the conventional polishing plates of Politexand IC-1000.

[0055] A dishing amount was evaluated by using a semiconductor structureshown in FIG. 3 as a sample to be polished. As shown in the drawing, thesemiconductor structure consisted of a silicon substrate 21, a siliconoxide film 22 formed on the silicon substrate 21 and having recesses,and an aluminum film 23 formed on the entire surface of the siliconoxide film 22. The aluminum film 23 was 800 nm thick, and the siliconoxide film 22 was 700 nm thick. Further, each of the recesses formed inthe silicon oxide film 22 was 400 nm deep. A width A of the recess and adistance B between the two adjacent recesses were set to meet therelationship: A/(A+B)≅0.7. The dishing amount was evaluated for thecases where the width A of the recess was set at 10 μm and 100 μm.

[0056] To be more specific, the aluminum film 23 was polished until thepolished surface reached a curve 23 b so as to evaluate the dishingamount. Table 2 shows the results of the evaluation: TABLE 2 Width ofWidth of Polishing wiring wiring cloth Conditioning (A = 10 μm) (A = 100μm) Politex none 160 nm >350 nm IC-1000 none 200 nm  250 nm IC-1000scratch  80 nm  210 nm Polishing none  8 nm  40 nm cloth of presentinvention Polishing scratch  20 nm  80 nm cloth of present invention

[0057] In the case of using the conventional polishing cloth of Politex,which is a very soft polishing cloth, the dishing amount was very large,i.e., 160 nm in the case where the width of the wiring was only 10 nm,and more than 350 nm in the case where the width of the wiring was 100nm.

[0058] In the case of using the conventional polishing cloth of IC-1000to which a conditioning treatment was applied, the dishing amount wassuppressed to 80 nm (A=10 μm) and 210 nm (A=100 nm), which are smallerthan those in the case of using Politex. However, these values aremarkedly larger than those in the case of using the polishing cloth ofthe present invention. A soft surface layer is formed on the polishingcloth IC-1000 by the conditioning treatment so as to give an adverseeffect to the flatness of the polished surface. Therefore, it appearsreasonable to understand that the dishing amount is diminished in thecase where a conditioning treatment is not applied to IC-1000. However,the dishing amount in the case where a conditioning treatment was notapplied to IC-1000 was found to be 200 nm (A=10 μm) and 250 nm (A=100μm), which are clearly larger than those in the case where theconditioning treatment was applied.

[0059] It should be noted in this connection that, if a conditioningtreatment is not applied, a deep scratch deeper than 20 nm is formed onthe surface of the aluminum film, and the aluminum film is eroded suchthat the scratch is enlarged, leading to the large dishing amount aspointed out above.

[0060] On the other hand, in the case of using the polishing cloth 10 ofthe present invention to which a conditioning treatment was not applied,the dishing amount was found to be only 8 nm in the case where the widthA of the recess was set at 10 μm and to be only 40 nm in the case wherethe width A of the recess was set at 100 μm. Clearly, the polishingcloth of the present invention permits markedly improving the dishingamount.

[0061] To reiterate, the polishing cloth 10 of the present inventioncomprises the very hard base body 11 having a compression modulus ofelasticity of 10 GPa. In addition, the polishing cloth 10 has a softsurface layer. It follows that scratches are not generated on thepolished surface of the target object. Also, a slurry is heldsufficiently on the soft surface of the polishing cloth. Further, thesoft surface layer is controlled to be very thin. These conditions areconsidered to have diminished the dishing amount in the case of usingthe polishing cloth of the present invention.

[0062] Incidentally, the dishing amount was found to be 20 nm (A=10 μm)and 80 nm (A=100 μm) in the case of using the polishing cloth 10 of thepresent invention to which a conditioning treatment was applied. Theconditioning treatment is considered to have further softened the softsurface layer and/or to have increased the thickness of the soft surfacelayer so as to increase the dishing amount.

[0063] A polishing rate of an aluminum film was evaluated by varying thediameter of the water-soluble filler 12. In each of the test cases, thepolishing cloth was prepared by setting the concentration of thewater-soluble fillers at 25% by weight. Table 3 shows the results: TABLE3 Filler diameter Polishing rate (nm/min)  1 μm 420  5 μm 2050 10 μm2200 30 μm 1400 50 μm 950 100 μm  800

[0064] Table 3 clearly shows that the polishing rate is dependent on thediameter of the water-soluble filler 12. Where the filler diameter wasset at 1 μm, a large number of scratches were generated on the polishedsurface of the aluminum film. It should be noted that the concavitiesformed on the surface of the polishing plate are unduly small where thefiller diameter is 1 μm, resulting in failure to form a soft surfacelayer on the polishing cloth 10. Also, where the concavities formed onthe surface are unduly small, the polishing cloth fails to retain theslurry sufficiently. As a result, numerous scratches were generated onthe polished surface of the aluminum film.

[0065] On the other hand, the polishing rate was low in the case wherethe filler diameter was set at 50 μm or 100 μm. The low polishing rateis considered to have been caused by the phenomenon that concavitiesformed on the surface of the polishing cloth were unduly large. Theexperimental data shown in Table 3 clearly support that the diameter ofthe water-soluble filler should desirably fall within a range of betweenabout 5 μm and 30 μm.

[0066] As described above, the polishing cloth of the present inventioncomprises a soft surface layer having a large number of concavitiesformed therein and an inner layer consisting of a base body and a largenumber of water-soluble fillers dispersed in the base body. Theparticular construction of the polishing cloth produces prominenteffects. To reiterate, the soft surface layer including a large numberof concavities permits improving the polishing rate and suppressing thescratch formation. At the same time, the hard inner layer permitsimproving the flatness of the polished surface of the target object.

[0067] What should also be noted is that, even if the surface layer ofthe base body is abraded during the polishing treatment, otherwater-soluble fillers are newly exposed to the surface of the polishingcloth so as to be dissolved in water or slurry. It follows that a softsurface layer is kept formed on the polishing cloth, making it possibleto obtain a stable polishing rate.

[0068] An additional feature of the present invention to be noted isthat, since a soft surface layer is formed, it is substantiallyunnecessary to apply a conditioning treatment to the polishing cloth soas to increase the life of the polishing cloth.

[0069] (Second Embodiment)

[0070]FIG. 4 is a cross sectional view showing the construction of apolishing cloth according to a second embodiment of the presentinvention. Those members of the polishing cloth shown in FIG. 4 whichare equal to those shown in FIG. 2 are denoted by the same referencenumerals so as to omit an overlapping description.

[0071] The polishing cloth of the second embodiment is featured in thata coating layer 31 made of a material insoluble in water (slurry) isformed to cover the outer surface of the water-soluble filler 12.

[0072] Where a large amount of the water-soluble filler is dispersed inthe base body, the filler particles tend to be brought into mutualcontact within the base body with a high probability. If the polishingcloth in which filler particles are in mutual contact is brought intocontact with water, a large and deep concavity 41 is formed, as shown inFIG. 5.

[0073] In the second embodiment of the present invention, however, allthe water-soluble fillers 12, which are in mutual contact, are notdissolved in the solvent because of the presence of the coating layer31. Naturally, the concavity formed on the surface does not extend deepinto the base body, making it possible to prevent the compressionmodulus of elasticity of the polishing cloth from being lowered.

[0074] The present invention is not limited to the embodiments describedabove. For example, in each of the embodiments described above, the basebody is formed of polystyrene, and the water-soluble filler is formed ofcellulose. However, other materials can also be used for forming thesebase bodies and the water-soluble fillers.

[0075] It is also possible to disperse a liquid material into the basebody in place of the solid water-soluble fillers. The liquid material,which is certainly softer than a solid material, is sufficiently hard,compared with a gaseous material, making it possible to use a liquidmaterial in place of the water-soluble filler. Of course, the liquidmaterial exposed to the surface of the base body flows out of the basebody so as to form concavities in the regions in which the liquidmaterial was sealed previously. It follows that the liquid materialdispersed in the base body produces an effect similar to that producedby the solid water-soluble filler.

[0076] In the embodiments described above, the fine particles dispersedin the base body are soluble in water. However, it is also possible todisperse fine particles that are soluble in a solvent other than waterin the base body. It suffices to spray a solvent capable of dissolvingthe fine particles against the surface of the polishing cloth beforeperforming the polishing treatment so as to dissolve the fine particlesdispersed in the base body so as to form concavities on the surface ofthe polishing cloth.

[0077] A method of manufacturing a semiconductor device having adamascene wiring structure involving a wiring groove will now bedescribed. The polishing cloth of the present invention described aboveis employed in the manufacture of the particular semiconductor device.

[0078] Specifically, FIG. 6 is a partial cross sectional view showing adamascene wiring structure in which an Al wiring 3 was buried in awiring groove 2 formed in a SiO₂ substrate 1. The wiring groove 2 had adepth of 4,000 Å and a width of 100 μm. Also, the thickness of the Allayer included in the Al wiring 3 was 8000 Å before the polishingoperation.

[0079] It should be noted that the Al wiring 3 is buried in the wiringgroove 2, and the surface of the Al wiring 3 is polished by thepolishing cloth of the present invention. In this case, the Al wiring 3is over-polished such that the upper surface of the Al wiring 3 ispositioned within the wiring groove 2 that is lower than the uppersurface of the SiO₂ substrate 1 so as to bring about a so-called“dishing” or “thinning”. As a result, a dishing is brought about.

[0080] In this embodiment, the flatness of the polished surface of theAl wiring 3 was evaluated under a load of 300 g/cm² and the rotatingspeed of the table and the carrier set at 50 rpm. The scratches formedon the Al wiring 3 buried in the wiring groove 2 were evaluated by KLA,with the result that 42,328 scratches/wafer were observed in the case ofusing the conventional polishing cloth of IC-100 in contrast to only 320scratches/wafer in the case of using the polishing cloth of the presentinvention.

[0081]FIG. 7 is a graph showing that the polishing cloth of the presentinvention is markedly superior to the conventional polishing cloth inthe effect of suppressing the dishing occurrence. To be more specific,the number of dishings that took place in the case of polishing the Alwiring 3 with the conventional polishing cloth of IC-1000 exceeded 3,500dishings (Å) when the over-polishing reached 60% of the depth of thewiring groove 2, as seen from the dotted line shown in FIG. 7.

[0082] On the other hand, a slurry prepared by dispersing in water 3% byweight of Al₂O₃, 1% by weight of (NH₄)₂S₂O₈ and 0.02% of benzotriazolewas retained on the surface of the polishing cloth of the presentinvention having fine particles dispersed in a base body. In the case ofpolishing the surface of the Al wiring 3 with the polishing cloth of thepresent invention noted above, the number of dishings occurring on thesurface of the polished Al wiring 3 scarcely increased even when theover-polishing reached 60% of the depth of the wiring groove 2 as seenfrom the solid line shown in FIG. 7. The experimental data clearlysupport that the quality and the characteristics of the Al wiring 3 wereimproved by the polishing treatment in the case of using the polishingcloth of the present invention. In other words, the wiring was formedsatisfactorily.

[0083]FIG. 8 is a partial cross sectional view showing a damascenewiring structure in which an Cu wiring 4 was buried in a wiring groove 2formed in a SiO₂ substrate 1. The wiring groove 2 had a depth of 4,000 Åand a width of 100 μm. Also, the thickness of the Cu layer included inthe Cu wiring 4 was 8,000 Å before the polishing operation.

[0084]FIG. 9 is a graph showing that the polishing cloth of the presentinvention is markedly superior to the conventional polishing cloth inthe effect of suppressing the dishing occurrence. To be more specific,the number of dishings that took place in the case of polishing the Cuwiring 4 with the conventional polishing cloth of IC-1000 approached3,500 dishings (Å) when the over-polishing reached 60% of the depth ofthe wiring groove 2, as seen from the dotted line shown in FIG. 9.

[0085] On the other hand, a slurry prepared by dispersing in water 1% byweight of Al₂O₃, 1% by weight of (NH₄)₂S₂O₈ and 0.05% of benzotriazolewas retained on the surface of the polishing cloth of the presentinvention having fine particles dispersed in a base body. In the case ofpolishing the surface of the Cu wiring 4 with the polishing cloth of thepresent invention noted above, the number of dishings occurring on thesurface of the polished Cu wiring 4 increased only slightly even whenthe over-polishing reached 60% of the depth of the wiring groove 2 asseen from the solid line shown in FIG. 9.

[0086]FIG. 10 is a partial cross sectional view showing a damascenewiring structure in which a W wiring 5 was buried in a wiring groove 2formed in a SiO₂ substrate 1. The wiring groove 2 had a depth of 4,000 Åand a width of 100 μm. Also, the thickness of the W layer included inthe W wiring 5 was 8,000 Å before the polishing operation.

[0087]FIG. 11 is a graph showing that the polishing cloth of the presentinvention is markedly superior to the conventional polishing cloth inthe effect of suppressing the dishing occurrence. To be more specific,the number of dishings that took place in the case of polishing the Wwiring 5 with the conventional polishing cloth of IC-1000 exceeded 3,500dishings (Å) when the over-polishing reached 60% of the depth of thewiring groove 2, as seen from the dotted line shown in FIG. 11.

[0088] On the other hand, a slurry prepared by dispersing in water 3% byweight of Al₂O₃ and 5% by weight of Fe(NO₃)₃ was retained on the surfaceof the polishing cloth of the present invention having fine particlesdispersed in a base body. In the case of polishing the surface of the Wwiring 5 with the polishing cloth of the present invention noted above,the number of dishings occurring on the surface of the polished W wiring5 increased only slightly even when the over-polishing reached 60% ofthe depth of the wiring groove 2 as seen from the solid line shown inFIG. 11.

[0089] An additional experiment was conducted as another embodiment ofthe present invention. In this experiment, an oxide film 6 having athickness of 14,000 Å was formed on a Si substrate 1 having a wiringgroove 2 formed on the surface in a depth of 7,000 Å and a width of 100μm, as shown in FIG. 12. The upper surface of the oxide film 6 thusformed was polished with the polishing cloth of the present invention.The slurry used in the polishing step was prepared by diluting SC-1manufactured by Cabot Inc. with pure water twice as much as SC-1.

[0090] The experimental data are shown in a graph of FIG. 13 in terms ofthe relationship between the remaining step (Å) and the oxide removal(Å). A dotted line shown in FIG. 13 represent the polishing with theconventional polishing cloth of IC-1000. On the other hand, the solidline in FIG. 13 represents the polishing with the polishing cloth of thepresent invention. As apparent from FIG. 13, the solid line representingthe use of the polishing cloth of the present invention is closer to anideal curve than the dotted line representing the use of theconventional polishing cloth of IC-1000. It follows that the polishingcloth of the present invention permits flattening the surface of anoxide film more uniformly than the conventional polishing cloth ofIC-1000.

[0091] The present invention can be worked in variously modifiedfashions within the technical scope of the present invention.

[0092] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

1. A polishing cloth, comprising: a base body holding a slurry on thesurface and serving to mechanically polish a surface of a target objectto be polished; and fine particles dispersed in said base body andsoluble in a solvent.
 2. The polishing cloth according to claim 1,wherein said base body includes fine concavities resulting fromdissolution of said fine particles in a solvent and formed on thesurface of said base body.
 3. The polishing cloth according to claim 1,wherein a coating layer insoluble in said solvent is formed to cover theouter surfaces of the fine particles.
 4. The polishing cloth accordingto claim 1, wherein voids are not present inside said base body.
 5. Thepolishing cloth according to claim 1, wherein at least one of SiO₂,Al₂O₃ and chemicals (oxidizing agent) is dispersed in water in saidslurry.
 6. The polishing cloth according to claim 1, wherein said fineparticles have a particle diameter of 5 to 30 μm.
 7. A polishing cloth,comprising: fine particles soluble in a solvent; and a base body havingsaid fine particles dispersed therein and holding a slurry on thesurface, said fine particles being dissolved in said solvent when asurface of a target object is mechanically polished by said polishingcloth so as to form concavities on the surface of the polishing cloth.8. The polishing cloth according to claim 7, wherein a coating layerinsoluble in said solvent is formed to cover the outer surfaces of thefine particles.
 9. The polishing cloth according to claim 7, whereinvoids are not present inside said base body.
 10. The polishing clothaccording to claim 7, wherein at least one of SiO₂, Al₂O₃ and chemicals(oxidizing agent) is dispersed in water in said slurry.
 11. Thepolishing cloth according to claim 7, wherein said fine particles have aparticle diameter of 5 to 30 μm.
 12. A method of manufacturing asemiconductor device by using a polishing cloth, comprising the stepsof: forming an insulating film on a substrate, followed by forming awiring groove on said substrate through said insulating film; forming ametal wiring layer on the substrate and in said wiring groove; buryingsaid metal wiring in said wiring groove; and polishing mechanically themetal wiring buried in said wiring groove with a polishing cloth so asto remove an undesired portion of the metal wiring and, thus, to flattenthe surface of the metal wiring, said polishing cloth comprising a basebody holding a slurry on the surface and serving to mechanically polisha surface of a target object to be polished, and fine particlesdispersed in said base body and soluble in a solvent.
 13. The method ofmanufacturing a semiconductor device by using a polishing clothaccording to claim 12, wherein said metal wiring contains Al as a maincomponent.
 14. The method of manufacturing a semiconductor device byusing a polishing cloth according to claim 12, wherein said metal wiringcontains Cu as a main component.
 15. The method of manufacturing asemiconductor device by using a polishing cloth according to claim 12,wherein said metal wiring contains W as a main component.
 16. A methodof manufacturing a semiconductor device by using a polishing cloth,comprising the steps of: forming a groove in a substrate; forming aninsulating film on said substrate such that said insulating film isburied in said groove; and polishing the insulating film by using apolishing cloth so as to remove an undesired portion of the insulatingfilm, thus, to flatten the surface of the insulating film, saidpolishing cloth comprising a base body holding a slurry on the surfaceand serving to mechanically polish a surface of a target object to bepolished, and fine particles dispersed in said base body and soluble ina solvent.
 17. The method of manufacturing a semiconductor device byusing a polishing cloth according to claim 16, wherein said oxide filmis a SiO₂ film.